The present invention relates to the use of oligomeric carbodiimides comprising at least one heterocyclic end group as stabilizers for polymers. The invention further relates to processes for stabilizing polymers against hydrolysis by adding oligomeric carbodiimides. The invention further provides selected carbodiimides and mixtures comprising oligomeric carbodiimides, further additives and/or polymers.
Further embodiments of the present invention will be apparent from the claims, the description and the examples. It would be appreciated that the features of the invention subject matter which are recited hereinabove and which are yet to be elucidated hereinbelow can be used not only in the particular concrete combination recited but also in other combinations without departing the scope of the invention. Embodiments of the present invention where all the features of the invention subject matter have the preferred and very preferred meanings are more particularly also preferred and very preferred, respectively.
Monomeric carbodiimides are known for use as hydrolysis stabilizers (U.S. Pat. No. 5,439,952). However, their use frequently gives rise to toxic by-products such as phenyl isocyanates. Oligomeric or polymeric carbodiimides are used in order to avoid toxicity issues.
DE 3217440 for example describes polyethylene terephthalates having improved resistance to hydrolysis and they comprise polycarbodiimides.
DE 198 09 634 A1 describes processes for preparing carbodiimides and mixtures comprising carbodiimides and polyesters or polyurethanes.
Carbodiimides comprising silane groups attached via urea groups and also mixtures thereof with polymers are described in WO 2005/111048 A1.
EP 0 507 407 A1 describes multifunctional water-dispersible crosslinking agents based on oligomeric substances comprising carbodiimide and other reactive functional groups, for example heterocycles. Aqueous dispersions, emulsions or solutions of such crosslinking agents and also processes for preparing the crosslinking agents are also described.
Oligomeric or polymeric carbodiimides are believed to be less toxic than monomeric carbodiimides because of lower by-product volatility. However, oligomeric or polymeric carbodiimides are frequently also less stabilizing than monomeric carbodiimides.
The present invention therefore has for its object to provide stabilizers on the basis of carbodiimides that do not have the abovementioned issues. It is more particularly an object of the present invention to provide carbodiimides that have a comparable stabilizing effect to monomeric carbodiimides without having the toxic potential of the latter.